<!DOCTYPE html>
<html>
<head>
<meta charset="utf-8">
<title></title>
<script >
function count(){
    var a = parseInt(document.getElementById("tex1").value);
    var b = parseInt(document.getElementById("tex2").value);
    var selectSign = document.getElementById("select").value;

    switch (selectSign)
    {
    case '+': answer = a+b;break;
    case '-': answer = a-b;break;
    case '*': answer = a*b;break;
    case '/': answer = a/b;
    }
    document.getElementById("fruit").value = answer;
    }
</script>
</head>
<body>
<input type="text" id="tex1" />
<select id="select">
<option value="+">+</option>
<option value="-">-</option>
<option value="*">*</option>
<option value="/">/</option>
</select>
<input type="text" id="tex2" />
<input type="button" value=" = " onclick="count()" />
<input type="text" id="fruit" onclick="count()" />
</body>
</html>